Method and device for testing maturity of hydrocarbon source rock

Abstract

The invention relates to a hydrocarbon source rock maturity testing method and device, and the testing method comprises the steps: S1, sequentially carrying out mechanical cutting and argon ion polishing on a hydrocarbon source rock sample, so that the sample has a flat polished surface; s2, acquiring a secondary electron image or a back scattering image of the polished surface of the sample; s3, extracting organic matters and organic apertures based on the secondary electron image or the back scattering image of the sample; s4, constructing an apparent organic matter conversion index by using the organic aperture surface porosity and the organic matter percentage obtained by the electron microscope image; s5, testing in the step S1 to the step S4 is repeated on the hydrocarbon source rock samples with different maturity degrees, and the corresponding relation between the apparent organic matter conversion index and the hydrocarbon source rock maturity degrees is established; s6, testing the apparent organic matter conversion index of the hydrocarbon source rock to be tested, and determining the maturity of the hydrocarbon source rock sample according to the corresponding relation. The maturity of different hydrocarbon source rocks is accurately tested by using the apparent organic matter conversion index, and exploration and development of oil and gas can be scientifically evaluated and guided.

Description

Technical Field

[0001] The present invention relates to the field of testing the maturity of hydrocarbon source rocks, and particularly to a method and device for testing the maturity of hydrocarbon source rocks. Background Art

[0002] As an unconventional energy source with huge global resource potential, shale oil and gas have received great attention from various countries. With the expansion of the oil and gas supply-demand gap in China and the continuous increase in the degree of external dependence, it has become extremely urgent to accelerate the exploration and development of shale oil and gas resources in China.

[0003] The formation of shale oil and gas depends on a series of processes such as the generation, deposition, diagenesis, and preservation of organic matter. In this series of processes, under the action of temperature and other factors, part of the organic matter is converted into hydrocarbons, and a part of the converted hydrocarbons is discharged from the organic matter, forming pores, namely organic pore fissures, on the surface of the organic matter. The maturity of organic matter is usually used to evaluate the hydrocarbon generation potential of hydrocarbon source rocks. Commonly used methods include vitrinite reflectance, rock pyrolysis, Raman and other methods. These methods are relatively mature and widely used, but such methods are complex to operate and cannot intuitively and simply test the maturity of hydrocarbon source rocks.

[0004] The Chinese patent "A Method and Device for Determining the Maturity of Hydrocarbon Source Rocks" with the patent number CN116008503A provides a relationship chart of the pyrolysis parameter Tmax of hydrocarbon source rocks and the vitrinite reflectance Ro of hydrocarbon source rocks. These charts can characterize the use of Tmax data to accurately evaluate the magnitude of the maturity value of hydrocarbon source rocks in a region.

[0005] The Chinese patent "A Method for Determining the Maturity of Hydrocarbon Source Rocks" with the patent number CN110412144B proposes to determine the maturity of hydrocarbon source rocks by quantitatively analyzing the relative content of ethyl noradamantane compounds using a comprehensive two-dimensional gas chromatography time-of-flight mass spectrometer and comparing it with the relative content of ethyl noradamantane compounds with known hydrocarbon source rock maturity.

[0006] The Chinese patent "A Method and Device for Predicting the Maturity of Hydrocarbon Source Rocks Based on 3D Seismic Data" with the patent number CN112327357A proposes to determine the maturity of hydrocarbon source rocks based on the relationship between the seismic waveform in 3D seismic data and the shale porosity and on the basis of the pre-established relationship between shale porosity and vitrinite reflectance.

[0007] Therefore, how to intuitively and simply test the maturity of hydrocarbon source rocks is an urgent problem to be solved in this field. Summary of the Invention

[0008] The present invention solves the problem of the lack of an intuitive and simple method for testing the maturity of hydrocarbon source rocks, and provides a method and device for testing the maturity of hydrocarbon source rocks to solve this technical problem. By characterizing the pore and fracture information in shale, the organic matter maturity is evaluated, the relationship between maturity and the development of organic pores and fractures is intuitively explained, and the maturity of different hydrocarbon source rocks is accurately tested using the apparent organic matter transformation index, so as to scientifically evaluate and guide the exploration and development of conventional and unconventional oil and gas.

[0009] To solve the above technical problems, the technical solution of the present invention is as follows:

[0010] A method and device for testing the maturity of hydrocarbon source rocks, including the following steps:

[0011] S1: Mechanically cut and argon ion polish the hydrocarbon source rock sample in sequence to form a flat polished surface on the sample;

[0012] S2: Put the polished sample into a scanning electron microscope to obtain a secondary electron image or a backscattered image of the polished surface of the sample;

[0013] S3: Based on the secondary electron image or backscattered image of the sample, select a region in the secondary electron image or backscattered image, obtain the total number of pixel points in the selected region, and then extract the number of pixel points of organic matter and organic pores and fractures (only these two are extracted) in the selected region to calculate the proportion of organic matter in the selected region: percentage of organic matter (AOM) and the proportion of organic pores and fractures in the selected region: pore and fracture surface porosity of organic matter (POM);

[0014] S4: Use the electron or backscattered image to calculate the pore and fracture surface porosity of organic matter (POM) and the percentage of organic matter (AOM) to construct an apparent organic matter transformation index (OMI);

[0015] S5: Repeat the tests of steps S1 to S4 on hydrocarbon source rock samples with different maturities to establish the corresponding relationship between OMI and the maturity Ro of hydrocarbon source rocks;

[0016] S6: Test the hydrocarbon source rock to be measured to obtain the apparent organic matter transformation index (OMI) of the hydrocarbon source rock to be measured, and determine the maturity of the hydrocarbon source rock sample according to the corresponding relationship between OMI and Ro.

[0017] Preferably, in step S3, a constant threshold method is used to calculate the percentage of organic matter (AOM) and the pore and fracture surface porosity of organic matter (POM), and a threshold algorithm is used to extract the pixel points of organic matter and organic pores and fractures, and the percentage contents of organic matter and organic pores and fractures are statistically calculated:

[0018] The percentage content of organic matter is Aom:

[0019] Aom = (∑ao ij) / (∑a ij )

[0020] Among them, ∑a ij represents the total number of pixel points scanned and statistically analyzed in the selected area, and ∑ao ij represents the total number of pixel points corresponding to organic matter in the selected area;

[0021] The percentage content of organic pores and fissures is pom:

[0022] Pom = (∑ap ij ) / (∑a ij )

[0023] Among them, ∑a ij represents the total number of pixel points scanned and statistically analyzed in the selected area, and ∑ap ij represents the total number of pixel points corresponding to organic pores and fissures in the selected area.

[0024] Preferably, the method for calculating the organic pore and fissure surface porosity (POM) and the organic matter percentage (AOM) further includes: the organic petrology method.

[0025] Preferably, in step S4, the formula for constructing the apparent organic matter transformation index (OMI) is:

[0026] OMI = Pom / (Pom + Aom)*100.

[0027] Preferably, when considering the compression effect of burial depth on the rock, the formula for the apparent organic matter transformation index (OMI) is:

[0028] OMI = f·Pom / (Pom + Aom)*100

[0029] Among them, f is the pressure correction coefficient caused by burial depth.

[0030] Preferably, in step S5, the corresponding relationship between the OMI and the maturity Ro of the sample constructed is:

[0031] Ro = ae b·OMI

[0032] The a and b in the formula are constants obtained by fitting.

[0033] Preferably, when repeating the tests of steps S1 to S4 on hydrocarbon source rock samples with different maturities, the samples used are hydrocarbon source rock samples from the same area and with the same geological conditions.

[0034] Preferably, the flatness of the polished surface formed after argon ion polishing needs to meet the requirements for nano imaging by scanning electron microscopy.

[0035] A testing device applicable to the above-mentioned hydrocarbon source rock maturity testing method, wherein the testing device includes a sample cutting and polishing module, an imaging module, and a calculation module, and specifically:

[0036] Sample cutting and polishing module: configured to execute step S1;

[0037] Imaging module: configured to execute step S2;

[0038] Calculation module: configured to execute steps S3 to S6.

[0039] Beneficial technical effects of the technical solution of the present invention:

[0040] The present invention uses the sample after argon ion polishing to perform electron imaging in a scanning electron microscope, distinguishes the organic matter and organic pore fissures on the polished surface of the sample according to the gray value in the image, and obtains the quantitative information of the organic matter and its internal pore fissures. The present invention defines a new parameter: apparent organic matter conversion index. By combining the apparent organic matter conversion index with the maturity of the hydrocarbon source rock measured by the existing method, the corresponding relationship between the apparent organic matter conversion index (OMI) and the maturity Ro of the hydrocarbon source rock can be obtained. Thus, in the subsequent testing process, the maturity of the organic matter can be evaluated according to the pore fissure information in the shale, the relationship between the maturity of the hydrocarbon source rock and the development of organic pore fissures is intuitively explained, and the maturity of different hydrocarbon source rocks can be accurately tested, so as to scientifically evaluate and guide the exploration and development of conventional and unconventional oil and gas. Description of the Drawings

[0041] Figure 1 Shows the flow chart of the testing method for the maturity of hydrocarbon source rocks in the embodiment of the present invention;

[0042] Figure 2 Shows the electron image of the shale scanning electron microscope in the embodiment of the present invention;

[0043] Figure 3 Shows the organic matter image extracted in the embodiment of the present invention;

[0044] Figure 4 Shows the organic pore fissure image extracted in the embodiment of the present invention;

[0045] Figure 5 Shows the curve graph of the corresponding relationship between OMI and Ro obtained in the embodiment of the present invention;

[0046] Figure 6 Shows the structural diagram of the testing device for the maturity of hydrocarbon source rocks in the embodiment of the present invention.

[0047] Marks in the drawings:

[0048] 1 - Sample cutting and polishing module; 2 - Imaging module; 3 - Calculation module. Detailed Embodiments

[0049] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the following further elaborates in detail a method and device for testing the maturity of a hydrocarbon source rock proposed by the present invention in conjunction with the accompanying drawings and specific embodiments. According to the following description, the advantages and features of the present invention will be clearer. It should be noted that the accompanying drawings are in a very simplified form and all use non-precise scales, only for the purpose of conveniently and clearly assisting in explaining the objectives of the embodiments of the present invention. In order to make the objectives, features and advantages of the present invention more obvious and understandable, please refer to the accompanying drawings. It should be noted that the structures, scales, sizes, etc. shown in the drawings of this specification are only used to cooperate with the content disclosed in the specification for those skilled in this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention. Therefore, they do not have a substantial technical meaning. Any modification of the structure, change of the proportional relationship or adjustment of the size, without affecting the effects that the present invention can produce and the objectives that can be achieved, should still fall within the scope covered by the technical content disclosed by the present invention.

[0050] The following will Figures 1 to 6 elaborate in detail the technical solutions of a method and device for testing the maturity of a hydrocarbon source rock of the present invention in conjunction with the accompanying drawings and specific embodiments.

[0051] Embodiment

[0052] As Figures 1 to 5 shown, a method for testing the maturity of a hydrocarbon source rock in this embodiment includes the following steps:

[0053] S1: Mechanically cut and argon ion polish the hydrocarbon source rock sample in sequence to form a flat polished surface on the sample;

[0054] S2: Place the polished sample into a scanning electron microscope to obtain a secondary electron image or a backscattered image of the polished surface of the sample;

[0055] S3: Based on the secondary electron image or backscattered image of the sample, select a region in the secondary electron image or backscattered image, obtain the total number of pixel points in the selected region, and then extract the number of pixel points of organic matter and organic pore spaces (only these two are extracted) in the selected region to calculate the proportion of organic matter in the selected region: organic matter percentage (AOM) and the proportion of organic pore spaces in the selected region: organic pore space surface porosity (POM);

[0056] S4: Use the electron or backscattered image to calculate the organic pore space surface porosity (POM) and the organic matter percentage (AOM) to construct an apparent organic matter conversion index (OMI);

[0057] S5: Repeat the tests of steps S1 to S4 on source rock samples with different maturities, and establish the corresponding relationship between OMI and the maturity Ro of the source rock;

[0058] S6: Test the source rock to be measured to obtain the apparent organic matter transformation index (OMI) of the source rock to be measured, and determine the maturity of the source rock sample according to the corresponding relationship between OMI and Ro.

[0059] Specifically, taking the shale sample as an example, use an argon ion polishing machine to polish the shale sample. In this embodiment, the argon ion polishing machine of Beiguang Technology Company is used to polish at a voltage of 2 kV to 6 kV to obtain a very flat surface. However, it should be understood that the present invention is not limited to using the argon ion polishing machine of Beiguang Technology Company, and products of other manufacturers can also be used for polishing, as long as it is ensured that the polished surface can be smoothly imaged nanoscopically.

[0060] Put the shale sample into a scanning electron microscope for scanning. When imaging the sample, in this embodiment, a field emission electron microscope of Zeiss Company is used, with a voltage of 1.5 kV, and a secondary electron probe is used to collect secondary electron signals to obtain Figure 2 the secondary electron image of the shale sample as shown. As Figure 2 shown, there may be minerals visible to the naked eye, organic matter, organic pores, inorganic pores and other features in the image.

[0061] After extracting the organic matter and the pores inside the organic matter, the traditional constant threshold method can be used to calculate POM and AOM. As Figure 3 shown, the black part represents the organic matter; Figure 4 shown, the black part represents the pores of the organic matter. The threshold algorithm is used to extract the pixel points of the organic matter and the organic pores, and the percentage contents of the organic matter and the organic pores are statistically calculated:

[0062] The percentage content of the organic matter is Aom:

[0063] Aom = (∑ao ij ) / (∑a ij )

[0064] where ∑a ij represents the total number of pixel points scanned and statistically calculated in the selected area, and ∑ao ij represents the total number of pixel points corresponding to the organic matter in the selected area;

[0065] The percentage content of the organic pores is pom:

[0066] Pom = (∑ap ij ) / (∑a ij )

[0067] where ∑a ijRepresents the total number of pixel points for scanning statistics in the selected area, ∑ap ij Represents the total number of pixel points corresponding to organic pore fractures in the selected area.

[0068] Of course, other methods can also be used to calculate the organic pore fracture surface porosity (POM) and the organic matter percentage (AOM), such as the organic petrology method.

[0069] Construct the apparent organic matter transformation index (OMI) using the organic pore fracture surface porosity (POM) and the organic matter percentage (AOM) obtained from secondary electron images or backscattered images:

[0070] OMI = Pom / (Pom + Aom) * 100

[0071] In addition, considering that burial depth may compress the rock, a pressure correction coefficient f due to burial depth should also be determined, as follows:

[0072] OMI = f · Pom / (Pom + Aom) * 100

[0073] Figure 2 Shown is the result with the apparent organic matter transformation index (OMI) being 5 and the pressure correction coefficient f = 1.

[0074] Subsequently, establish the corresponding relationship between OMI and the maturity Ro obtained by conventional methods. Through this corresponding relationship, the maturity of the source rock sample can be directly determined according to OMI during subsequent testing. Specifically, for example, establish the corresponding relationship between the OMI of the sample and the maturity Ro of the sample measured by conventional methods through the following formula:

[0075] Ro = ae b·OMI

[0076] a and b are constants obtained by fitting depending on actual data. It should be noted that due to different geological conditions of source rocks in different basins and regions, the relationship will change. When repeating the tests of steps S1 to S4 on source rock samples with different maturities, source rock samples from the same region with the same geological conditions should be used to calculate the accurate a and b constants.

[0077] For example, when a takes the value of 0.6 and b takes the value of 0.04, as Figure 5 shown, when OMI = 5, Ro is approximately equal to 0.7.

[0078] During the maturation process of shale, a part of the hydrocarbons generated will be expelled, leaving pores and fractures in the organic matter. By characterizing the pore and fracture information in the organic matter, the maturity of the organic matter can be evaluated. The relationship between the apparent organic matter transformation index OMI and the maturity Ro proposed in the present invention can intuitively explain the relationship between maturity and the development of organic pores and fractures. The maturity of different source rocks is scientifically and effectively indicated by the apparent transformation index of the organic matter, so as to better scientifically evaluate and guide the exploration and development of conventional and unconventional oil and gas in China.

[0079] Figure 6 A test device applicable to the above-mentioned source rock maturity test method is shown. The device includes a sample cutting and polishing module 1, an imaging module 2, and a calculation module 3.

[0080] Sample cutting and polishing module 1: Configured to execute step S1. The sample cutting and polishing module includes a mechanical cutting machine and an argon ion polishing machine;

[0081] Imaging module 2: Configured to execute step S2. The imaging module is a scanning electron microscope;

[0082] Calculation module 3: Configured to execute steps S3 to S6. The calculation module is a computer or other electronic device with a program for executing steps S3 to S6.

[0083] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0084] The above-described embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it cannot be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A test method for the maturity of a hydrocarbon source rock, characterized in that, It includes the following steps: S1: Mechanically cut and argon ion polish the source rock sample in sequence to form a flat polished surface on the sample; S2: Put the polished sample into a scanning electron microscope to obtain a secondary electron image or a backscattered image of the polished surface of the sample; S3: Based on the secondary electron image or backscattered image of the sample, select an area in the secondary electron image or backscattered image, obtain the total number of pixel points in the selected area, and then extract the number of pixel points of organic matter and organic pore spaces (only these two are extracted) in the selected area to calculate the proportion of organic matter in the selected area: organic matter percentage (AOM) and the proportion of organic pore spaces in the selected area: organic pore space surface porosity (POM); S4: Use the electron or backscattered image to calculate the organic pore space surface porosity (POM) and the organic matter percentage (AOM) to construct an apparent organic matter transformation index (OMI); S5: Repeat the tests of steps S1 to S4 on source rock samples with different maturities to establish the corresponding relationship between OMI and the maturity Ro of the source rock; S6: Test the source rock to be measured to obtain the apparent organic matter transformation index (OMI) of the source rock to be measured, and determine the maturity of the source rock sample according to the corresponding relationship between OMI and Ro.

2. The testing method for the maturity of a hydrocarbon source rock according to claim 1, characterized in that, In step S3, a constant threshold method is used to calculate the organic matter percentage (AOM) and the organic pore space surface porosity (POM), and a threshold algorithm is used to extract the pixel points of organic matter and organic pore spaces, and the percentage contents of organic matter and organic pore spaces are statistically calculated: The percentage content of organic matter is Aom: Aom = (∑ao ij ) / (∑a ij ) Among them, ∑a ij represents the total number of pixel points scanned and counted in the selected area, and ∑ao ij represents the total number of pixel points corresponding to organic matter in the selected area; The percentage content of organic pore spaces is pom: Pom = (∑ap ij ) / (∑a ij ) where ∑a ij represents the total number of pixel points scanned and statistically analyzed in the selected area, and ∑ap ij represents the total number of pixel points corresponding to the organic pores and cracks in the selected area.

3. The testing method for the maturity of a hydrocarbon source rock according to claim 1, characterized in that, The method for calculating the organic pore space surface porosity (POM) and the organic matter percentage (AOM) also includes: the organic petrology method.

4. The method for testing the maturity of a hydrocarbon source rock according to claim 1, wherein The formula for constructing the apparent organic matter transformation index (OMI) in step S4 is: OMI = Pom / (Pom + Aom) * 100.

5. The method for testing the maturity of a hydrocarbon source rock according to claim 4, characterized in that, When considering the compression effect of burial depth on the rock, the formula for the apparent organic matter transformation index (OMI) is: OMI = f · Pom / (Pom + Aom) * 100 where f is the pressure correction coefficient caused by burial depth.

6. The test method for the maturity of a hydrocarbon source rock according to claim 1, characterized in that, The corresponding relationship between the OMI and the maturity Ro of the sample constructed in step S5 is: Ro = ae b·OMI a and b in the formula are constants obtained by fitting.

7. The method for testing the maturity of a hydrocarbon source rock according to claim 1, wherein When repeating the tests of steps S1 to S4 on source rock samples with different maturities, the samples used are source rock samples from the same area and with the same geological conditions.

8. The method for testing the maturity of a hydrocarbon source rock according to claim 1, characterized in that, The flatness of the polished surface formed after argon ion polishing needs to meet the requirements for nano imaging by the scanning electron microscope.

9. A testing device applicable to the testing method for the maturity of the hydrocarbon source rock according to any one of claims 1 to 8, characterized in that, The test device includes a sample cutting and polishing module, an imaging module, and a calculation module, where: Sample cutting and polishing module: Configured to execute step S1; Imaging module: Configured to execute step S2; Calculation module: Configured to execute steps S3 to S6.

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